17.beta.-estradiol is often used for treating estrogen deficiency. This deficiency origins from e.g. oophorectomy, menopause, radiation-induced ovarian failure, panhypopituitarism and Kallman's syndrome.
When taken orally 17.beta.-estradiol is relatively ineffective (1,2). Besides, oral estrogens effect the liver proteins due to portal absorption (3), the intestinal metabolism (4,5) and "bolus" surges of circulating estrogen after each dose (5).
The problem with oral estrogen therapy can be avoided by vaginal administration and steroids are well absorbed from vagina. The administration of 17.beta.-estradiol via intravaginal devices has been suggested and thoroughly studied (6,7,8,9). One of these studies, viz. the study by Englund et al (7), discloses intravaginal devices having an in vitro release rate of 200 .mu.g/24 h, which corresponded to plasma levels in the women varying between 80-200 pg/ml. In the end of the article it is concluded that the release rate of 200 .mu.g per day is too high for replacement therapy in postmenopausal women as they exceed the estrogen levels seen in the follicular phase in fertile women. It is suggested that devices releasing 50-100 .mu.g of 17.beta.-estradiol per day might deliver the proper dosage.
In the articles by Stumpf (6,9) and Veldhuls (8) the release rates per day are not discussed but the plasma levels disclosed are in the range of 50-150 pg/ml, which is about the same magnitude as disclosed in the Englund article.